Schistosomes of the Schistosoma haematobium (terminal spine egg) complex recently have been recognized as biologic agents for induction of bladder cancer in several nonhuman primates. Mechanisms leading to or factors influencing bladder pathology which may lead to cancer are poorly understood. It has been assumed, based on epidemiologic evidence, that duration of exposure to schistosomes and their products may be significant in bladder carcinogenesis. A group of 45 capuchin monkeys (Cebus apella), consisting of 30 S. haematobium infected hosts and 15 controls, has been followed for approximately 4 years to determine the effects of prolonged infections on host-parasite relationships and bladder pathology. These animals have been followed closely to provide a parasitologic profile for infected subjects and to relate this to fluctuations in bladder pathology. The status of host-parasite relationships and bladder involvement have been judged by (1) passage of schistosome eggs with excreta, (2) cellular elements in urine cytology preparations, (3) X-ray examination of the urogenital tract, (4) examination of the bladder by cystotomy of selected hosts, and (5) biopsy of necropsy samples examined for viruses, when appropriate. Monitoring of the parasitologic and pathologic aspects of S. haematobium infection will continue for 1 more year after which there will be a compilation of data. BIBLIOGRAPHIC REFERENCES: Experimental bilharzial bladder cancer: Tryptophan metabolism in nonhuman primates experimentally infected with Schistosoma haematobium. R. R. Brown, R. E. Kuntz, R. A. Arend, J. A. Moore, and T. C. Huang. J. Nat. Cancer Inst. 56:101-104, 1976. Carcinoma of the urinary bladder in Schistosoma haematobium infection. Animal model: proliferative urothelial lesions in nonhuman primates infected with Schistosoma haematobium. A. W. Cheever, R. E. Kuntz, J. A. Moore, G. T. Bryan, and R. R. Brown. Am. J. Path. 84: 673-676, 1976.